Corrosion inhibiting composition



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CORRGSION COIVIPOSITION No Drawing. Application May 3, 1955 Serial No. 505,857

6 Claims. (Cl. 252-387) The present invention relates to corrosion inhibition. In particular, the invention is concerned primarily with inhibiting coirosion in water circulation systems where the water comes in contact with ferrous metals such as iron and steel. However, it has also been found very eflective for inhibiting corrosion of such metals as copper, brasss, bronze and other non-ferrous metals, and for couples of such metals with ferrous metals.

The invention is an improvement based upon the known fact that phosphates in small added quantities will assist in inhibiting underwater corrosion. In addition, it is known that if a cyanide is added with the phosphates, improved corrosion inhibiting effects are achieved.

The invention stems from the discovery that if chromates are added to phosphates and cyanides in aqueous solution, superior corrosion inhibition results. The beneficial results of the invention may be achieved in solutions containing such corrosive ions as sulphates and chlorides in varying concentrations.

Accordingly it is a principal object of the present invention to furnish an improved corrosion inhibiting composition. An allied object of the invention is to furnish such a corrosion inhibitor which is readily and completely soluble in water.

Another object of the invention is to furnish a corrosion inhibitor which operates to prevent corrosion on ferrous and other metals at elevated temperatures by corrosive water.

Still another object of the invention is to provide a corrosion inhibitor which is adaptable to treat water high in chloride content and/or high in mineral content.

Other objects and advantages will become apparent as the description of the invention and various illustrative embodiments proceeds.

The synergistic anodic corrosion inhibitors illustrative. of the invention are prepared by intimately mixing. corrosion inhibiting phosphates, including the polyphosphates and orthophosphates, cyanides, complex cyanides or organic nitriles, and chromates. Especially good results have been achieved with monosodium phosphate anhydrous (Nat -1 1 sodium, ferrocyanide though a dry mix of the ingredients has been found satisfactory in a wide variety of commercial applications, the inhibitor may also be packaged in briquette and solution. The present invention contemplates the combination ingredients in whatever form they may be introduced into the system.

In order to evaluate the invention a testing apparatus atet and procedure was developed. The testing apparatus comprised a pyrex glass aspirator bottle of four liter capacity serving as a reservoir. Three liters of tap water, or synthetic water adjusted to the desired pH, controlled to include the proper proportion of corrosive material and residual of the inhibitor to be tested were placed within the reservoir. A variable temperature electric heating element in contact with the reservoir was adjusted to maintain the solution therein at a temperature of ISO-160 F.

The corrosion test coupon was then inserted in a large tube interposed in the discharge line from the pump circulating from and to the reservoir bottle so that it was in constant contact with the moving fluid. The test coupon was a 3" length of diameter cold drawn steel (CI-I018) rod with rounded ends. very nearly the average composition of ordinary black iron pipe. After having been given a suitable surface treatment, the coupons were weighed to the fourth decimal place on an analytical balance.

A rate-of-flow indicator was placed in the circulatory system immediately following the test coupon and the rate adjusted by a needle valve or equivalent device to provide a velocity of fluid passing over the coupon within the range of 0.2 to 0.25 foot per second.

During the runs the pH of the water in the system, the inhibitor residual, and the volume of fluid in the system was adjusted at least twice a day. The rate of flow and temperature of the fiuid were checked at more frequent intervals commensurate with maintaining their appropriate operational ranges. All tests were run for five days.

After completing a run, the coupons were then cleaned, dried with a clean cloth, baked in an oven at C. for one hour and cooled in a desiccator. The coupons were then weighed to the fourth decimal place on an analytical balance and the loss of weight determined. The loss of weight was converted to average penetration in inches per year (IPY) according to the accepted formula. This can, of course, be readily con verted to mils per year (MPY) by shifting the decimal point.

The following examples, having been evaluated by the test procedure described above, are set forth to fur-- EXAMPLE I A corrosion inhibiting composition was prepared by mixing dry forty (40) parts of monosodium phosphate (anhydrous), two (2) parts of potassium ferricyanide, twenty-five (25) parts of sodium dichromate (hydrous), and thirty-three (33) parts of sodium sulphate (anhydrous). After dry mixing these quantities thoroughly they were added to the water to be tested so that there were 12 to 16 parts per million dichromate, 16 to 20 parts per million of P0 ion, 1.0 to 1.3 parts per million ferricyanide and a pH of between 5.5 and 7.5. Where herein and hereafter we employ the language parts per million or ppm. we intend the same to have its recognized meaning in this art, namely milligrams per liter.

The water employed was Chicago, Illinois, tap water having an average partial composition as follows:

Ion: Rpm. Calcium 30 Magnesium 10 Chloride 8 Sulphate 17 pH 8.2.

This steel has- The water, after adding the corrosion inhibitor, was adwere used as the corrosion inhibitor. Results expressed justed to a pH of 6.5 with sulphuric acid. The sulphate as penetration, inches per year are compared with those content of the Water is raised by an average of about 45 obtained in the test cited in Example I.

parts per million by employing sulphuric acid to adjust TEST A the'pH. Depending upon the parts per million concen- [Inhibitor-Sodium dichromate (NazGrgO7.2HaO)0ommercial.]

tration of the corrosion inhibitor the following test results were obtained: Results of Test Results from Example I P P t Inhibitor, Penetration Percent Inhibitor, Penetra- Per- Inhibitor 3 Inhibitor ppm 1? p.p.m. in. per yr. Inh. p.p.m. tion, 111. cent 1 7 per year per yr. Inh.

300 0. 00127 30 0. 00134 0. 00750 70 0. 00063 91. 6 0. 00209 72. 2 85 0. 00061 91. 9 400 0.00067 50 00074 0. 00134 82. 2 100 0. 00059 92. 2 00074 2 V This test indicates that, weight for Weight, and under the same conditions, the composition given in Example I is at least eight times as ath h l v 1 Percentage of inhibition ficient as sodium dic romate (hydrous) w an used a one TEST B This test indicated that not over 50 parts per million Of [Inhibitor-Commercial glassy sodium polyphosphate (anhydrous) the inhibitor would be required to give satisfactory inessenmuy hibition with Chicago tap water. 2O

1 Results of Test Results from Example I EXAMPLE II c Inhibitor ppm. Penetration, Inhibitor, p.p.m. Penetration, In order to determine the optimum pH at which to Per Y -P operate a cooling system in which the inhibitor is emv ployed another series of tests was performed with Chicago figfg? 50 g gg tap water adjusted to various values of pH with sulsmall pits) absent) phuricacid. Throughout this series of tests the concentration of the inhibitor was held at a resid al of 50 parts This test indicates that, under the same conditions, the composition given in Example I is more than five times as effective as the polyphosp61 mill-10D The esults W as followsphate alone, weight for weight, since it also prevents pitting.

TEST 0 [Inhibitor-A mixture consisting of 90 parts glassy sodium polyphosphate (anhydrous) essentially Na PmOn', approx. 85% P0 and 10 parts potassium ierricyanide,

This test indicates that, under the same conditions, a mixture of 90% glassy polyphosphate and 10% potassium i'erricyanide is more etiicient, weight for weight, than the phosphate when used alone, but is much less efiicient than the mixture used in Example I and moreover, does not prevent pitting.

) Inhibitor residual 50 p.p.m. 7 EXAMPLE IV P 015 Water: Penetration P 3' In order to determine the eifectiveness of the inhibitor .3- 009 86 in water having a high mineral concentration a series 0-00344 50 of tests was run at pH 6.5 on a synthetic water made up 5-0 0- from Chicago tap water having the following partial 6.0 0.00092 analysis; 7.0 1 0.00073 8.0 2 0.00062 1 Trace of scale detectable at 100 dia magnification Calclum 925 '9 Very light deposit oi scale visible to naked eye. Magnesium 200 Chloride 3800 From the foregoing two examples and other tests which have been performed the following conclusions may be Sulphate 2200 drawn: 1 PH (1) A concentration of 50 ppm. of the inhibitor is When this water was adjusted to pH 6.5 with sulphuric sufiicient for good inhibition at pH values between 5.0 acid the sulphate content was raised to about 2650 p.p.m.

and 8.0. In the corrosion test with this water, the pH was held at (2) Results obtained at pH 6.0 and 7.0 indicate that 6.5 which the foregoing examples indicated to be within the optimum for good protection lies between these the optimum range, and the concentration of the inhibivalues, but effective inhibition results both below and tor was varied. The results obtained were as follows: above the pH range of 6.0 to 7.0. r

XA P n Inhibitor, p.p.m. Penetration, Percent In order to illustrate the synergistic effect the various m per yr. Lnmbmon components of the mixture given in Example I have 0 @0546 upon each other when used for the inhibition of cor- 0:00198 "553 rosion, the following results were obtained in the labora- 8' 32-2 tory. vIn all tests Chicago tap water adjusted to pH 6.5 0100032 with sulphuric acid was circulated in the apparatus 211- ready described in. Example I, and control was the same, No scale deposition could be detected on any of the but only one, or a pair of the components of the. mixture 75 coupons at diameters magnification, indicating that 5 a pH of 6.5 is sufficiently low to prevent deposition in this highly mineralized water.

EXAMPLE V In order to determine the inhibiting properties of this material in the presence of high chloride but otherwise low mineral content, another series was run in Chicago tap water containing various concentrations of chloride, the desired chloride concentration being obtained by the addition of sodium chloride. Tests were run at pH 6.5 with a concentration of 50 p.p.m. of inhibitor throughout the series. Results are tabulated below.

Penetration Penetration Percent Chloride, p.p.m. Without With Inb., Inhibition Inhibitor, in. per year Calculated in. per yr.

EXAMPLE VI In the petroleum industry where rigid requirements obtain for a corrosion inhibitor, the following formula gave excellent results:

Parts Disodium phosphate (anhydrous) 26 Monosodium phosphate (anhydrous) 18 Sodium dichromate 24 Sodium ferrocyanide 2 Sodium sulphate 30 The foregoing was controlled to 50 p.p.m. at a pH of 6 to 6.5.

In this industry the upper limit of satisfactory performance of a corrosion inhibitor is a corrosion rate of 0.005 IPY. In actual use in cooling towers at an operating refinery over a period of 90 days the average penetration rate was 0.0011 IPY as determined by 19 test coupons at various locations therein, or about one fifth the acceptable limit. The maximum rate was 0.0020 IPY and the minimum penetration rate shown was 0.0004 IPY.

From the foregoing examples and conclusions reached as well as many other tests which have been performed, the following conclusions as to the etlicacy of, and treatment with, the inhibitor may be drawn:

(1) The inhibitor is highly efiective within a pH range of 5.0 to 8.0 (optimum about 6.5) and somewhat beyond these values.

(2) In water low in chloride, sulphate and mineral content (such as Chicago tap water) a residual of between 40 and 60 p.p.m. (optimum about 50 p.p.m.) provides excellent inhibition.

(3) If the water to be treated is high in chloride content 50 to 60 p.p.m. of the inhibitor will also give excellent corrosion inhibition.

(4) If the water to be treated is high in both chloride and other mineral matter, a residual of 50 p.p.m. of the inhibitor will give as good or better inhibition than it does in a water low in these constituents.

Other examples of preparations which have exhibited highly effective corrosion inhibition are:

Parts Sodium ferrocyanide 4 Glassy polyphosphate 10 Sodium dichromate 60 Sodium sulphate (anhydrous) 26 Parts Sodium polyphosphate 25 Sodium ferrocyanide 20 Sodium dichromate 15 Soda ash 40 W Parts Monosodium phosphate 20 Disodium phosphate 40 Sodium dichromate 33 Sodium ferrocyanide 3 Sodium sulphate 4 Parts Disodium phosphate 8 Caustic potash 6 Sodium ferrocyanide 14 Sodium dichromate 10 Water 62 Parts Monosodium phosphate 13 Potassium ferricyanide 5 Sodium dichromate 15 Water 67 NorE.--The caustic potash aids in the preparation of the product.

Some of the ortho-phosphates employed satisfactorily are disodium phosphate, tri-sodium phosphate, sodiumpotassium phosphate, ammonium phosphates, and other soluble ortho-phosphates.

Monosodium phosphate has been found satisfactory in application when used to the exclusion of disodium phosphate. It has been observed, however, that by including the disodium phosphate additional corrosion preventive action takes place. In view of this observation, the ratio between the monosodium and disodium phosphates does not appear to be critical, but it has been observed that when the disodium phosphates are approximately twice the weight of the monosodium phosphates, excellent results are achieved.

Polyphosphates such as hexametaphosphate, tripolyphosphate, pyrophosphates and the glassy polyphosphates commercially available have proved equally satisfactory as the other phosphates. No water soluble phosphates have been found unsatisfactory for application in the inhibitor.

Many complex cyanides have been employed in the inhibitor, commercial sodium ferrocyanide having been found to give excellent results with easy control and low cost as additional advantages. Other complex cyanides which may be employed are soluble ferricyanides, nitroferricyanides and also organic nitriles.

Among others, the chromates which have been found to perform satisfactorily in the inhibitor are chromic acid, sodium dichromate (bichromate), potassium dichromate (bichromate) and other water soluble chromate compounds such as those of calcium and magnesium. No water soluble chromic acid compounds were found unsatisfactory.

The ratios of the various constituents of the inhibitor can vary considerably with relationship to each other as well as the total weight of the inhibitor, just as the total weight of the inhibitor may vary'withrespect to the amount of water being treated. Also, it has been found that inert materials such as sodium sulphate or soda ash may be employed with the inhibitor to prevent any caking or cohesion of the mixed dry ingredients in transit when prepared in that form.

The.foregoing tests described, as well as additional ones performed, indicate that although the various elements of the inhibitor employed alone will have certain very limited corrosion-inhibiting action, their combined corrosion protection at elevated temperatures far exceeds their individual or paired effect. This discovery of the combined corrosive inhibiting action of these various compositions could not have been predicted from the general knowledge in this field of chemistry, and particularly their advantageous and economic use under varying field conditions. V

Although one particular embodiment of the invention has been shown and described in full here, there is no intention to thereby limit the invention to the details of such embodiment. On thecontrary, the intention is to cover all modifications, alternative embodiments, usages and equivalents of the corrosion inhibitor as fall within the spirit and scope of the invention, specification and appended claims. a i

We claim as our invention:

1. A corrosion inhibiting composition consisting essentially of a water-soluble inorganic polyphosphate, a water-soluble inorganic complex cyanide, and a watersoluble inorganic chromate, said ingredients being present inparts, by weight, as follows:

i Parts Water-soluble inorganic polyphosphate 8 to 40 Water-soluble inorganic complex cyanide 2 to 25 Water-soluble inorganic chromate 10 to 65 p 2. A corrosion inhibiting composition consisting es- 'sentially of a Water-soluble inorganic phosphate, a watersoluble inorganic complex cyanide, and a water-soluble inorganic'chromate, said ingredients being present in parts, by weight, as follows:

Parts Water-soluble inorganic phosphate 8 to 40 Water-soluble inorganic complex cyanide 2 to 25 Water-soluble inorganic chromate 10 to 65 8 3. A corrosion inhibiting composition consisting essentially of a water-soluble inorganic orthophosphate, a. water-soluble inorganic complex cyanide, and a water-- soluble inorganic chromate, said ingredients being present in parts, by weight, as follows:

, Parts Water-soluble inorganic orthophosphate. 8 to 40 Water-soluble inorganic complex cyanide 2 to 25 Water-soluble inorganic dichromate 10 to 4. A corrosion inhibiting composition consisting essentially of the following in the stated parts by weight:

. I Parts Monosodium phosphate 10 to 40 Sodium dichromate 25 to 65 Potassium ferricyanide '2 to 25' 5. A corrosion inhibiting composition consisting essentially of the following ingredients in substantially the following parts by weight: w i

Parts Disodium phosphate 26. Monosodium phosphate 18 Sodium dichromate 24 Sodium ferrocyanide 2 6. A corrosion inhibiting composition consisting essentially of 40 parts anhydrous monosodium phosphate, 25 parts hydrous sodium dichromate, and 2 parts sodium ferrocyanide, said parts being by weight. 

1. A CORROSION INHIBITING COMPOSITION CONSISTING ESSENTIALLY OF A WATER-SOLUBLE INORGANIC POLYPHOSPHATE, A WATER-SOLUBLE INORGANIC COMPLEX CYANIDE, AND A WATER SOLUBLE INORGANIC CHROMATE, SAID INGREDIENTS BEING PRESENT IN PARTS, BY WEIGHT, AS FOLLOWS: WATER-SOLUBLE INORGANIC POLYPHOSPHATE----------8 TO 40 WATER-SOLUBLE INORGANIC COMPLEX CYANIDE---------2 TO 25 WATER-SOLUBLE INORGANIC CHROMATE--------------10 TO 65 